I can send e-mail but not recive?

I whent trough the perfect server setup for centos 4. I installed the roundcube package from isp and the email worked perfect. after i wanted to be avail to log in to webmail on webmail.domain.com so i follow that tutorial. and after that my email stop recieving email. it sends but not recive. after that i delete it the webmail subdomain and re-install the roundcube package but i can make it recieve e-mail.